Dremel Fix ?

[trbig]

I don't have a hardness tester either, but I've done enough of these that I know there's a difference in the surface steel when you start grinding and the softer steel underneath. I use a carbide bit to do mine. When you start, there's not much progress, but just under the surface, it'll eat that metal in a hurry if you aren't careful.

TC, I don't know if others have said it, but I have said that after grinding, the gears and slots are just smeared blobs of metal mashed together. I rebuilt an engine once and did the gear grind. That motor only lasted 2500 miles, so I went back in and saw what was happening to the gears after the grinding them and running them. Back-cutting them is useless. The dogs/slots just smash together flat anyway, and all you've done by back-cutting is remove even more material. If you doubt the case hardness statement, look at a set of gears run for thousands of miles, then look at a set run just a couple thousand after grinding.

[TomB]

You will always find a level of work hardening on the surface of high mileage gear teeth and their dogs that give the appearance of case hardening.

I've done the dremel and washer fix and many other gear grinding jobs professionally and agree with Senrak, the gears look through hardened (better described as toughened as they're not that hard). I found the same on Suzuki gears. Old Triumphs on the other hand are case hardened and are very noticeable when ground, they give off yellow sparks turning very orange as you hit the softer inner metal, the case hardened gears can easily be re-case hardened when machining is complete, if you feel the need to case harden your Yamaha gears have a go, you'll probably end up making them softer in the process

Brinell hardness testing uses a ball bearing pushed into the metal at a fixed load, the diameter of the indent measured to tell hardness. I always use Rockwell C scale standard which uses a small pyramid in a similar manor, across the corners of the square indent measured, generally for harder metals than the Brinell test. Any Toolmaker will have done this stuff.

[trbig]

the case hardened gears can easily be re-case hardened when machining is complete, if you feel the need to case harden your Yamaha gears have a go, you'll probably end up making them softer in the process

I was told how to correctly re-harden the dogs, but you would either have to have a machinist do the gear grind so everything was EXACT, or put the gears back in after grinding and run them a short while so they seat together, then remove them again and harden.

If the gears are not case hardened, as you both say, why are gears that have run thousands upon thousands of miles still in pretty much their original shape, yet after grinding, and run just a couple thousand miles, the dogs AND slots are smashed and misshapen to such an extreme? Your theories don't hold up to real life experience.

[senrak]

If the gears are not case hardened, as you both say, why are gears that have run thousands upon thousands of miles still in pretty much their original shape, yet after grinding, and run just a couple thousand miles, the dogs AND slots are smashed and misshapen to such an extreme? Your theories don't hold up to real life experience.[/QUOTE]

trbig has a valid point.
If the dogs are beat up after grinding and use, it would stand to reason that the material in contact is softer. I don't really have the answer to that, but something is changing, and my guess is that trbig has more experience than I do.
My thinking is that how the transmission is treated after the Dremmel fix may be a big factor in how well it holds up. Things like waiting out the spin before shifting from neutral into 1st, being easy on acceleration, and just treating your tranny the way you would like to be treated could make a big difference in the success of the "fix".
trbig. I would be interested in learning more about the hardening process you mentioned. I can't think of anything that would be worse than being 500 miles from home with a tranny that doesn't work.

[trbig]

The hardening process I was told of was learned from a crotchety old man that owns a local welding supply shop, but they also had a welding shop on site. I had taken my engine case to them to get welded after I broke where the timing mechanism and cover attaches in a crash. He didn't have the eyesight any more, but he stood there and instructed his welder on how to fix that cast aluminum. This guy has forgotten more than I'll ever know. This was another time I'd gotten to see how misshapen the gears were since I took them just the case halves.

So, as we talked, I told him of the gear issues and the grinding, explaining the dogs/slots, etc. He told me that back in WW2, supplies were severely limited at the time and many times they had to make their own gears for ships and equipment. I'd asked him about building the material back up on the dogs with some hard-facing (VERY hard material used to edge excavation equipment). He shook his head and said that would be way too brittle. He said that I shouldn't worry about trying to build the dogs back up, but the way they would case harden things like just those dogs or just teeth on a gear would be to get a smallish flame with an acetylene torch and heat the dog to a nice cherry red, not "A big damned orange fireball!" as he said. After the dog gets red, shut off the oxygen knob on the torch so you just have that sooty acetylene flame and keep moving it around the dog until it was coated really well with that black soot. Then shut the torch off and let it cool. DO NOT QUENCH he said. As it cools, it will draw the carbon molecules into the top layer of the steel, hardening it.

By just working on the dogs, there shouldn't be any danger of warping the whole gear, according to him, especially if you let the gear cool between dogs.

[trbig]

I can't think of anything that would be worse than being 500 miles from home with a tranny that doesn't work.

Don't sweat that. It'll work just fine after the grind. Those two surfaces will smash together where they want to be and you'll probably never have to worry about it again. I've been less than nice to my transmissions and have been running this set of gears for over 100k miles now after the grind. And even if it went out, it would only be a gear, or worst case, two, not the whole tranny. It just honestly baffles me as to WHY it works after seeing the gears afterwards.

And thinking about this the last couple days, my line of thinking would be to grind the dogs and the slots,(I would personally grind them flat, not beveled) but just re-harden the dogs. This would leave a soft enough bed for the dogs to hit so that they all got seated squarely instead of breaking them. Much more metal in 2nd gear slots than those little dogs.

Just a thought...

[TomB]

I was told how to correctly re-harden the dogs, but you would either have to have a machinist do the gear grind so everything was EXACT, or put the gears back in after grinding and run them a short while so they seat together, then remove them again and harden.

If the gears are not case hardened, as you both say, why are gears that have run thousands upon thousands of miles still in pretty much their original shape, yet after grinding, and run just a couple thousand miles, the dogs AND slots are smashed and misshapen to such an extreme? Your theories don't hold up to real life experience.

Maybe as you say, the dogs need grinding very accurately and if they're not they will load one dog up a lot more than the others, therefore wearing it prematurely. When I do dog grinding I "blue" the dogs, fit the gears to the shaft and fit them together, trying every dog in every slot to ensure they all drive the same amount every time they engage.
A bad surface finish can lead to premature wear too, two rough ground finishes can have a galling effect, polished finishes fair better.

[tarzan]

I have a bit experience with hardening metals.
TRBIG, the process you describe, would actually "anneal" the material.Making it soft again.
If you want to re-harden material or change the hardness after it has been hardened, you have to anneal it first, and then heat treat it again to the desired hardness.
A lot of "old school" metal fabricators/machinist will "case harden" by heating raw material with a torch and then quenching in oil, or water. It's tough to get a real accurate depth or hardness that way, but it can be done.

BTW, I will try and remember to take my old gears to work and check hardness, I ground on them too, so I can test both, an area I ground on, and an area that I haven't ground.

[trbig]

I have a bit experience with hardening metals.
TRBIG, the process you describe, would actually "anneal" the material.Making it soft again.

That would be incorrect. I've spoken with many people about this process including the famous knife maker A.G. Russell at a gun show who agreed with the process. He even gave me his secret recipe for quenching a knife blade... BUT.. quenching would make the whole dog hard and brittle. XSChop, who's a chemical engineer, thinks it can be taken a step even further if you used cryo treatment (Extreme cold).As taken from the definition:

"...Adding that hard coating to steel is what case hardening is all about.In order to case harden steel you will need to heat the steal in the presence of carbon. It is the infusion of carbon into the outer layer of the steel which hardens it."

The process I described does exactly that, while keeping the inner section of the dog soft and a hard outside shell from the carbon introduced or sucked into the steel as it cools. After grinding, the dogs are not case hardened any more.


Oh, and checking the hardness of your old gears, you could check the ground face vs the top of the dog

[tarzan]

Annealing, in metallurgy and materials science, is a heat treatment that alters a material to increase its ductility and to make it more workable. It involves heating material to above its critical temperature, maintaining a suitable temperature, and then cooling. Annealing can induce ductility, soften material, relieve internal stresses, refine the structure by making it homogeneous, and improve cold working properties.

In the cases of copper, steel, silver, and brass, this process is performed by heating the material (generally until glowing) for a while and then letting it cool to room temperature in still air. Copper, silver[1] and brass can be cooled slowly in air, or quickly by quenching in water, unlike ferrous metals, such as steel, which must be cooled slowly to anneal. In this fashion, the metal is softened and prepared for further work—such as shaping, stamping, or forming.

[senrak]

After the dog gets red, shut off the oxygen knob on the torch so you just have that sooty acetylene flame and keep moving it around the dog until it was coated really well with that black soot. Then shut the torch off and let it cool. DO NOT QUENCH he said. As it cools, it will draw the carbon molecules into the top layer of the steel, hardening it.

The process that old timer was describing is what is called carburizing. It is widely used in industry today, be it more sophisticated. The parts are put in an atmosphere controlled oven, heated to temp and held there, sometimes for days and slowly cooled, usually in the oven, oxygen free.
Could work in this case. The source of the carbon is ingenious.

[skids]

OK, so what about "work hardening"? Like grind the thing, and ride the bike while shifting purposefully without racing through the gears until it is "broke in?"

[CaptonZap]

Better living through chemistry. I know Kasenit works, haven't tried the other brand.
http://www.midwayusa.com/Product/119479/cherry-red-surface-hardening-compound-1-lb
http://www.gunreports.com/special_re...eel1750-1.html

[trbig]

Annealing, in metallurgy and materials science, is a heat treatment that alters a material to increase its ductility and to make it more workable. It involves heating material to above its critical temperature, maintaining a suitable temperature, and then cooling. Annealing can induce ductility, soften material, relieve internal stresses, refine the structure by making it homogeneous, and improve cold working properties.

In the cases of copper, steel, silver, and brass, this process is performed by heating the material (generally until glowing) for a while and then letting it cool to room temperature in still air. Copper, silver[1] and brass can be cooled slowly in air, or quickly by quenching in water, unlike ferrous metals, such as steel, which must be cooled slowly to anneal. In this fashion, the metal is softened and prepared for further work—such as shaping, stamping, or forming.

And still disregarding everything about the introduction of carbon. You don't add carbon in annealing. It's completely absent in the process. Introducing carbon into heated steel and letting it cool is not annealing.

Skids, as for work hardening, I'm sure that's what's happening. If the dogs/slots kept smearing at the rate they do at the beginning of running them, this fix wouldn't last any time. It seems they stop the "Squishing" process at a certain point. Plus, with the addition of stress/friction on the gear, there will be heat, and the gear is rolling around in a bath of carbon. Not quite the temps for a normal case harden, but I'm sure it's there to an extent with the heating/cooling cycles the gears get.

[tarzan]

And still disregarding everything about the introduction of carbon. You don't add carbon in annealing. It's completely absent in the process. Introducing carbon into heated steel and letting it cool is not annealing...

LOL. You are stubborn. You really should try your method. Take a hardened gear that you ground on, then heat it up real hot, and shut the oxygen off ,covering it in soot,then let it cool.